This invention relates to systems for measurement and display of parameters and, more particularly, to apparatus for scaling and display of multiple parameter data from remote locations when the parameters have different ranges of values.
It is frequently necessary to monitor system or process parameters by displaying the parameter values at a location remote from the system or process. For example, in the fabrication of semiconductor devices, the processing equipment is typically located in a clean room, while the operator display and control can be located outside the clean room. Voltages, currents, vacuum levels, etc. are measured and transmitted to the remote display unit. Remote display units are utilized in numerous other applications. When data is transmitted over moderate or long distances, serial data transmission is almost always used to minimize the number of data transmission paths. In a typical system, the values of the measured parameters are converted to digital form and time multiplexed onto a serial data link for transmission to the remote display unit. The serial data link can be a pair of conductors, a telephone line or an optical fiber.
In general, the measured parameters have different ranges of values. For example, one parameter may be a voltage having a range from 0 to 4,000 volts, while while a second parameter may be a current having a range of values from 0 to 100 amps. The display system must be able to accurately measure and display the various parameters with a minimum of complexity.
Typically, the analog parameter values are converted to digital form by an analog-to-digital (A/D) converter before transmission over the serial line. In order to maintain maximum measurement accuracy, the full input range of the analog-to-digital converter must be utilized for each parameter. Therefore, different scale factors are associated with the parameter data for each parameter transmitted to the remote display unit.
Microprocessors can be used to properly scale the data received by the remote display unit and provide scaled display data. However, for low to moderate numbers of parameter measurements, the use of a microprocessor can be more complex than necessary.
It is an object of the present invention to provide a novel system for remote display of multiple measured parameters.
It is another object of the present invention to provide apparatus for scaling a data word representing one of a plurality of measured parameters depending on the range of values of the parameter.
It is yet another object of the present invention to provide apparatus for the display of measured parameters which apparatus is easily adaptable to display of parameters having different ranges of values.